So I killed one group boss and looted this dagger, which tells me it's unique and 'bind on pickup'.

Then I logged off the game, and when logged again I killed the same boss and got the same loot with info as above - unable to loot because item is "unique and you already have one".
Restriction that forbids it seems ridiculous in a game of this scale with so many looted items. Or maybe it's some bug?
In general what makes this item unique? I would give it for research or deconstruction only, like all blue items.
PC EU (PL): 14 characters. ESO player since 06.08.2015. Farkas finest quote: "Some people don't think I'm smart. Those people get my fist. But you, I like."